Green Twin Completed (home-cast engine by Pat J)

[GreenTwin]

After many long years, and a whole lot of trial and error, with much emphasis on error, I finally completed the green twin oscillator.
This engine began when another member sent me three photos of this engine, from the Preston's services website in England.

The initial game plan was to use this engine to try and learn 3D modeling.
I was able to complete the 3D model, and so my buddy who sent me the photos (woodguy) and I started to scheme about making a model from bar stock.
Then we started dreaming about a set of models cast in aluminum.
Then I said "Well, if we go to that much trouble, why not just cast the engine in gray iron?".

Be careful what you wish for, as they say.
8 short years later the green twin was done, as well as woodguy's "gray twin", which was built from the second set of castings I made.

Pretty much everything I did on this engine was a first for me.
Previous to this engine, I had done some partial engine builds for a group build, so I had a very steep learning curve.

My dream was to publish this engine build, along with complete drawings, and that finally happened this year with the March/April edition of Live Steam Magazine.
It has been a wild ride for sure.

Casting gray iron was really tricky, and in the end, the only parts that were cast in iron were the flywheels.
The remaining parts were cast in 356 aluminum.
If I knew then what I know now, all of the parts would have been cast in gray iron.

I tried to make a model that was as close to the original engine as I could get it, and custom made all the fasteners to look old-style.

I am pleased with how the engines (green and gray) turned out, but I am more pleased with what I learned during the build, especially mastering the art of making my own gray iron castings, as well as figuring out how to make patterns, write magazine articles, machine engine parts, etc.

The magazine article is a series, and so far three articles have been published, with one and perhaps two more to be published.
This was my first complete engine build.

 

[GreenTwin]

Pouring a flywheel in gray iron in the backyard.

 

[GreenTwin]

My furnace.
Burner uses an atomizing nozzle, with diesel as fuel.
Toro varialbe speed leaf blower as a combustion air source.

 

[johnmcc69]

Vert nice! Congrats on the article & your new found knowledge!

How big is this engine? Flywheel diameter?

John

 

[GreenTwin]

Thanks much.
The flywheel is 6" diameter.
It is a 60% scale of the original engine from England.

For me it was not really about building an engine, but learning how to build an engine.
I thoroughly enjoyed the whole experience, but I must say it was very trying at times.

Its a great hobby, and I can't wait to start another engine build.
.

 

[Steamchick]

Big CONGRATULATIONS on completing this engine. Originally, I think they were used in ships, but not very big ones. Small coasters and the like? You have done something most of us wouldn't consider in making your own cast iron parts. I have use scrap mazaK and aluminium for odd small castings. But yours are near industrial sized! Well done!
The only problem with aluminium cylinders and steam is corrosion. Especially with superheat. I recommend you get the aluminium parts HARD ANODISED (not the regular anodising, different chemistry and not suitable for steam engine bores). Bores and steam passages will corrode horribly otherwise.
But OK if you only run on air.
K2

 

[Jasonb]

I think those of us that have been about from the start of this project have always considered it a workshop engine which is what it was originally described as. Prestons are a good source of inspiration, at least two other engines they have had for sale have been made as models.

https://prestonservices.co.uk/item/oscillating-twin-cylinder-horizontal-workshop-engine/
Good to see you have finally got it into print now Pat, hope you are ready for a demand for casting sets! Though it could be made by other methods too.

 

[GreenTwin]

Big CONGRATULATIONS on completing this engine. Originally, I think they were used in ships, but not very big ones. Small coasters and the like? You have done something most of us wouldn't consider in making your own cast iron parts. I have use scrap mazaK and aluminium for odd small castings. But yours are near industrial sized! Well done!
The only problem with aluminium cylinders and steam is corrosion. Especially with superheat. I recommend you get the aluminium parts HARD ANODISED (not the regular anodising, different chemistry and not suitable for steam engine bores). Bores and steam passages will corrode horribly otherwise.
But OK if you only run on air.

Thanks much.
As I stated in the article, it all started when a fellow modeler (woodguy) showed me three photos of the Prestons green twin.
Woodguy had started a 3D model of the engine, but got bogged down with it, and was moving on to another engine.

So I started modeling the green twin in 3D just on a whim, in order to try and learn 3D well enough to use it for engine design.
The 3D design turned out well, and so woodguy and I discussed a bar-stock build.

It sort of escalated from there, with talk of making aluminum castings, and then wild scheming of making gray iron castings.
I had never done any foundry work, and knew nothing of pattern making, which is a bit of an art.

My first two iron pours were successful, but just barely, and I made the two flywheels.
When I tried to cast the cylinders and other thin parts in iron, I ended up with parts that had the hardness of tool steel, and even carbide would not cut them.
The flywheels machined easily, and so I had no idea why the iron suddenly was solidifying into something unmachinable.

I finally had to choose between getting the green twin casting finished in this lifetime, or spending some indefinite amount of time trying to figure out what was happening with the iron, with the very real possibility that I would never figure out the iron hardness problem.

So everything except the flywheels is 356 aluminum, tempered per a T6 specification.

The editor mentioned that anyone building one of these engines would probably want to sleeve the cylinder with an iron liner, use adonized aluminum as you mention, or otherwise make modifications to make the engine wear better.
I told the editor that for me, this build had little to do with making an engine that would wear well for a long time, but rather an endeavor to learn how to design an engine from three photos, how to make patterns, how to make sand molds, how to melt and pour metal, how to accurately machine parts and assemble them, and how to make accurate 2D drawings for it all.

The fact that this build did not finish me off completely is a miracle; it was most difficult because everything I did was basically a first for me, and this is the first complete engine I have ever built.
If felt like plowing frozen ground for many years (lots of broken plows and burnt hands), and I was about to give up on more than one occasion, and just accept abject defeat as my reality and my fate in the model building world.

I see this engine for me as a proof-of-concept thing, and a few years after all the parts had been cast, I finally did figure out how to cast thin parts in gray iron without getting hard metal.
I have been temped to just toss this engine and make a new one with iron, but I can't bring myself to do it because this engine represents the journey much more than it represents an engine.

What is important about this engine is the position it puts me in when I begin making the next engine (the O-S horizontal, which is the same one seen in Dave Richard's videos powering his lineshaft machine shop).
There will be no guesswork on the O-S engine, and that is a huge relief.

.

 

[GreenTwin]

Good to see you have finally got it into print now Pat, hope you are ready for a demand for casting sets! Though it could be made by other methods too.

At one point in time, I considered making production castings, but there are many reasons why I chose not to do that, most of which revolves around it becoming too much like work, and no longer being fun.

I have toyed with the idea of releasing the 3D model STL files to the modeling community, so they could try their hand at 3D printing patterns, making castings, and building this engine.
I have not made a decision about releasing the STL files.
I am not in it for the money, and I did not get paid for the Live Steam article.
The Live Steam article was my way of giving back to the modeling community that helped me in so many ways, and still helps me to this day.

The complete 2D drawings are included in the magazine article, and the engine could be built using the bar stock method, but this engine just begs to be cast, in my opinion.

I also still have the patterns for this engine, but they are not set up for a commercial foundry to use.
For a production run of castings for this engine, I think a set of matchplates would need to be made for all the parts.

Jason and many others have been around from when I started trying to build model engines (2012), guiding me on the in's and out's of model building.
I am very grateful for the information that I received from so many, here and other places.
The constant support and encouragement is what kept me going all those years.

Edit:
Note that the flywheel for the original green twin engine is listed in the Preston advertisement as 12" diameter, but it is actually 10" diameter.
I used a grid placed over the photos to get a proportion for the parts, and I started my design based on a 6" diameter flywheel, and proportioned everything from that, so the error in the stated flywheel size did not effect my engine design, luckily.

.

 

[GreenTwin]

Here is a comparison of the original Preston's green twin, my 3D model, and the model I built.
My intent was to build a model that was as close to the original as I could possibly get, and I was pleasantly surprised at how close I got it with only 3 photos as a guide.
Quite frankly, in the beginning, I had little confidence that I would pull any of this off; success was never a given, and I had never succeeded before with an engine build, so there was much doubt both in the beginning and throughout the build.

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[maverick]

Very nice job Pat. I remember the start of that project and had a printout of your early cad model hanging in my office till I shut down the shop. Really glad you stuck it out and completed the twin, it’s a very good lesson for some of us I’m sure.
Mike

 

[GreenTwin]

Mike-

Thanks for the kind comments.
It seems like eons ago when I started the green twin project, and there are many familiar faces I am seeing here from the past.

When the magazine articles are complete, I will issue the 11"-17" CAD drawings in pdf format to whoever requests a set, for personal use only.
The LS article does have complete CAD drawings, but the 11x17 set would be a bit easier to follow in my opinion.

I generally open-source all the engine CAD drawings I make, sooner or later, for free.
My intent is to promote the steam engine building hobby, and perhaps take it to new heights.

Great to hear from you.
I had to learn a ridiculous number of things on this build, but I feel like now I can better discuss model building with the experienced folks of model building.
Having actually built an engine, I can talk from experience, not from speculation.


Pat J
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